What Happens When You Look Through Binoculars Backwards?

[frederickcan]

Homework Statement

A pair of binoculars has a magnification of 7X. What would be their magnification if you were to look through them the wrong way, that is, through one of their objective lenses instead of the eyepieces?

Homework Equations

focal length
f = -L/M

The magnification of the objective lens.
M=-s'/s ~~ -L/f

The Attempt at a Solution

I'm really confused. I think I'm supposed to find the focal length first. Should I use the standard length of a microscope? (L=160mm)

This is what I attempted:
f= -160mm/-7 = 22.9 mm
M= -160 mm/22.9 mm = 6.99

 

[Redbelly98]

Not sure I follow what you're doing. Are you aware that each eye is looking through two lenses in a pair of binoculars? You'll need to account for the focal lengths of the two lenses somehow.

I would expect there is a discussion of either binoculars, or equivalently of telescopes, in your textbook or lecture notes.

 

[bm0p700f]

What is the formula for a pair of lens combined. There is one. Find it and all will be revealed.
(hint it involves focal length only).